Stealth Omicron Could Cause More Cases After BA.1 Wave, Says WHO Expert Maria Van Kerkhove

World Health Organization epidemiologist Maria Van Kerkhove has said the Omicron BA.2 sub-type is accounting for a growing proportion of COVID cases and could cause more infections.

BA.2, which is informally referred to as "Stealth Omicron," continues to spread after becoming the dominant COVID type in Denmark and South Africa in recent weeks. Infectious disease specialists have said it appears to be more transmissible than the generally dominant Omicron type BA.1.

BA.2's spread comes as the U.S. and other countries are recovering from a record-breaking winter spike in cases driven largely by Omicron.

Speaking at a press briefing on Wednesday, Kerkhove, the WHO's technical lead on COVID, said the agency was monitoring the current decline in cases around the world, but added: "We also need to look at: is there a slowing of that decline or will we start to see an increase again?

"What we're worried about is […] if we start to see an increase—and I'm not saying we are seeing this—we could see some further infections of BA.2 after this big wave of BA.1. I know a lot of people are concerned about this, but this is something that we are looking at."

Kerkhove also pointed out that the WHO had not seen "any difference in terms of severity" between BA.2 and BA.1.

Research is underway to find out the exact risk posed by BA.2. Earlier this week a study from Japan suggested the sub-variant could be more dangerous and immune-resistant than BA.1, based on animal and cell culture studies.

The Japanese researchers recommended that BA.2 be classified as a separate variant of concern. However, other experts have told Newsweek that results from animal studies are not necessarily of significance to humans.

Research from the U.K. has suggested that COVID vaccines are as effective against BA.2 as they are against BA.1 in terms of preventing symptomatic disease, based on people who have had a booster shot.

COVID cases are continuing to fall in the U.S. according to the Centers for Disease Control and Prevention. The seven-day moving average of new cases was 121,664 on Wednesday, down from 213,625 a week earlier.

The number of COVID deaths has also dropped in the past few days. The seven-day moving average of new deaths was 2,020 on Wednesday, down from 2,363 a week earlier, the CDC has reported.

About 214.5 million people in the U.S. are fully vaccinated—64.6 percent of the total population—and 92.4 million of those have received a booster dose.

COVID test
A health care worker in New York carries out a COVID test in December 2021. The WHO is monitoring BA.2, the sub-type known as "Stealth Omicron." Scott Heins/Getty